Liquid composition comprising two initiators, its process of polymerization, use and material or composition obtained following polymerization of composition

ABSTRACT

The present invention relates to a liquid composition comprising a monomer, a (meth)acrylic polymer and at least two initiators. In particular the present invention relates to a liquid composition comprising a monomer, a (meth)acrylic polymer and at least two initiators that have a different half life time. That liquid composition can be used as a syrup and especially as a syrup for impregnation of fibres or fibrous material. Also concerned is a thermoplastic material obtained after polymerization of the liquid composition. The invention also relates to a process for manufacturing such a liquid composition. The invention also relates to a process for impregnating a fibrous substrate of long fibres with said liquid composition. The invention also relates to a fibrous substrate impregnated with said liquid composition which is useful for manufacturing composite parts. The present invention also relates to a process for manufacturing mechanical parts or structural elements made of composite material and to mechanical parts or structural elements made of composite material obtained via a process using such a liquid composition.

This application claims benefit, under U.S.C. § 119 or § 365 of PCTApplication Number PCT/EP2017/084201, filed Dec. 21, 2017, and FrenchPatent Application Number FR16.63063, filed Dec. 21, 2016, thesedocuments being incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a liquid composition comprising amonomer, a (meth)acrylic polymer and at least two initiators.

In particular the present invention relates to a liquid compositioncomprising a monomer, a (meth)acrylic polymer and at least twoinitiators that have a different half life time. That liquid compositioncan be used as a syrup and especially as a syrup for impregnation offibres or fibrous material. Also concerned is a thermoplastic materialobtained after polymerization of the liquid composition. The inventionalso relates to a process for manufacturing such a liquid composition.The invention also relates to a process for impregnating a fibroussubstrate of long fibres with said liquid composition. The inventionalso relates to a fibrous substrate impregnated with said liquidcomposition which is useful for manufacturing composite parts.

The present invention also relates to a process for manufacturingmechanical parts or structural elements made of composite material andto mechanical parts or structural elements made of composite materialobtained via a process using such a liquid composition.

PRIOR ART

Thermoplastic polymers are materials that are widely used today inseveral fields and applications, for example in the construction,aeronautic, automobile or railway sectors, where they are part ofmechanical parts.

These mechanical parts that have to withstand high stresses during theiruse are widely manufactured from composite materials. A compositematerial is a macroscopic combination of two or more immisciblematerials. The composite material consists of at least one materialwhich forms the matrix, i.e. a continuous phase that ensures thecohesion of the structure, and a reinforcing material.

The purpose of using a composite material is to obtain performancequalities that are not available from each of its constituents when theyare used separately. Consequently, composite materials are widely usedin several industrial sectors, for instance building, automotive,aerospace, transport, leisure, electronics, and sports notably due totheir better mechanical performance (higher tensile strength, highertensile modulus, higher fracture toughness) and their low density, incomparison with homogeneous materials.

To allow thermoforming and recycling, it is preferred to usethermoplastic polymers also in composite materials.

Thermoplastic polymers consist of linear or branched polymers, which areusually not crosslinked. The thermoplastic polymers are heated in orderto mix the constituents necessary for manufacturing the compositematerial and are cooled to set the final form. The problem of thesemolten thermoplastic polymers is their very high viscosity. In order toprepare a polymeric composite material based on thermoplastic polymer, athermoplastic polymer resin, commonly known as a “syrup”, is used toimpregnate the reinforcing material, for example a fibrous substrate.Once polymerized, the thermoplastic polymeric syrup constitutes thematrix of the composite material.

At the time of impregnation, when preparing polymeric composites, theviscosity of the impregnation syrup must be controlled and adapted so asnot to be too fluid or too viscous, so as to impregnate correctly eachfibre of the fibrous substrate. When the wetting is partial, dependingon whether the syrup is too fluid or too viscous, “naked” zones, i.e.non-impregnated zones, and zones in which drops of polymer form on thefibres, which are the cause of the creation of bubbles, respectivelyappear. These “naked” zones and these bubbles give rise to theappearance of defects in the final composite material, which are thecause, inter alia, of a loss of mechanical strength of the finalcomposite material.

Also when used without impregnation, it is wished to have a liquidcomposition that polymerizes fast with a good conversion in order toincrease productivity.

A liquid composition or syrup comprising a (meth)acrylic monomer and a(meth)acrylic polymer is described in WO 2013/056845 and WO 2014/013028.The polymerization of the monomer(s) in both documents is achieved withradical generating initiator(s) or initiating systems comprising radicalgeneration initiator system(s). For both documents benzoyl peroxide isused in the examples.

The document WO2014/174098 discloses a liquid (meth)acrylic syrup. Thesyrup comprises an initiating system comprising an accelerator, anorganic aldehyde, one peracid and one liquid peroxy compound. Thepolymerization time in the examples of this document is hours or severaldozens of minutes.

The document WO2015/110534 discloses an impregnation process for afibrous substrate, a liquid monomer syrup for impregnating process, itsmethod of polymerization and structural article obtained thereof. Thedocument just discloses in a general manner a list of initiators andthat a combination of two of them might be used.

The document WO2013/056845 discloses a composite material via in-situpolymerization od thermoplastic (meth)acrylic resins. The document justdiscloses in a general manner a list of initiators and that acombination of two of them might be used.

The document U.S. Pat. No. 4,328,329 discloses a process forpolymerizing methyl methacrylate syrup using a dual initiator system.The process concerns a cast sheet process with cycle times of severaldozen minutes and temperature profile going 80° C. to 135° C. duringpolymerization. One of the used initiators is always2,2′-azobis(isobutyronitrile).

The document U.S. Pat. No. 4,605,717 discloses the preparation ofacrylic polymer sheets using a ternary peroxide initiator system. Theprocess uses two temperature ranges, from 45° C. to 90° C. for the firsttwo initiators and from 110° C. to 140° C. for a final cure with thethird initiator.

The document EP 0189930 discloses a process for preparing acrylicpolymers using a dual peroxide initiator system. The process uses twotemperature ranges, from 45° C. to 90° C. for 10 to 100 minutes for thefirst initiator and from 110° C. to 140° C. for 5 to 60 minutes a finalcure with the second initiator.

The document U.S. Pat. No. 5,151,482 discloses a process the productionof methecrylic resin sheets. In this process the two initiators areused. The process comprises also different temperature ramps, includingheating and cooling ramps and high temperature curing at the end.

The document U.S. Pat. No. 4,211,742 discloses a process for thecontinuous casting of liquid polymerizable compositions. Thepolymerization times are at least 15 minutes even if the sheet has athickness of 3 mm. The process comprises also different temperatureramps and high temperature curing at the end.

It is not suggested in any of these documents that incorporation of twoinitiators, into a liquid composition allows fast and completepolymerization, especially in short cycle times of less than 15 minutesand having low residual monomer content, especially process with simpletemperature profile.

TECHNICAL PROBLEM

The aim of the invention is thus to remedy at least one of the drawbacksof the prior art.

An objective of the present invention is to have a liquid compositioncomprising a monomer, a (meth)acrylic polymer and at least twoinitiators for having a composition that can be polymerized fast and toa good conversion. By a good conversion is understood that at least 95%of the monomers have been polymerized, preferably at least 99%. By fastis understood that the polymerization takes place in less than 15minutes, preferably less than 10 min, even more preferably less than 5min and advantageously less than 3 min.

An objective of the present invention is also to have a process forpolymerizing fast a liquid composition comprising a monomer, a(meth)acrylic polymer and at least two initiators to a good conversion.

Still another objective of the present invention is to use a liquidcomposition comprising a monomer, a (meth)acrylic polymer and at leasttwo initiators for having a fast polymerization and a good conversion,having residual monomer of less than 1% based on initially employedmonomer quantity.

The invention is also directed toward completely, correctly anduniformly wetting the fibrous substrate during the impregnation. Anydefects of fibre wetting, for example by bubbles and voids, decrease themechanical performance of the manufactured mechanical or structuredparts or articles or final composite part.

Another object of the present invention is to propose a process that canbe performed at low cost and that allows industrial-scale manufacture ofmechanical parts or structural elements made of thermoplastic polymer orthermoplastic composite material. In addition, the process should beeasy and simple to perform using commercially available compounds. Themanufacture of the composite parts should also be reproducible and fast,meaning short cycle times of less than 15 min, preferably less than 10min, even more preferably less than 5 min and advantageously less than 3min.

BRIEF DESCRIPTION OF THE INVENTION

It has been discovered, surprisingly, that a liquid compositioncomprising

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2);        said liquid (meth)acrylic syrup having a dynamic viscosity of        between 10 mPa*s and 10 000 mPa*s at 25° C., yields to a        thermoplastic polymer composition after polymerization of said        (meth)acrylic monomer (M1), said thermoplastic polymer        composition is having a fast kinetics and a high conversion of        the (meth)acrylic monomer (M1), in comparison to a composition        comprising only initiator (Ini1).

It has also been discovered that a liquid composition comprising

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2);        said liquid (meth)acrylic syrup having a dynamic viscosity of        between 10 mPa*s and 10 000 mPa*s at 25° C., can be used to        produce a thermoplastic polymer composition after polymerization        of said (meth)acrylic monomer (M1), said thermoplastic polymer        composition is having a low content of residual monomer, in        comparison to a composition comprising only one initiator as        (Ini1).

It has also been discovered that a liquid composition comprising

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2);        said liquid (meth)acrylic syrup having a dynamic viscosity of        between 10 mPa*s and 10 000 mPa*s at 25° C., can be used to        produce a thermoplastic polymer composition after polymerization        of said (meth)acrylic monomer (M1), much faster in comparison to        a composition comprising only one initiator as (Ini2).

It has been discovered as well that a liquid (meth)acrylic compositionfor impregnating a fibrous substrate, said fibrous substrate consistingof long fibres, said composition being characterized in that itcomprises:

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2);        said liquid (meth)acrylic syrup having a dynamic viscosity of        between 10 mPa*s and 10 000 mPa*s at 25° C.; gives total and        correct impregnation of the fibrous substrate.

The Applicant has also discovered, surprisingly, that an impregnationprocess for impregnating a fibrous substrate, said fibrous substrateconsisting of long fibres and said process comprising a step ofimpregnating said fibrous substrate with said liquid composition orliquid (meth)acrylic impregnation syrup, gives full and correctimpregnation of the fibrous substrate and allows fast and completepolymerization to good conversion, in comparison to a compositioncomprising only initiators (Ini1).

It has also been discovered, surprisingly, that a process formanufacturing composite parts, comprising the following steps:

-   -   i) impregnating a fibrous substrate with such a liquid        composition or (meth)acrylic syrup,    -   ii) polymerizing the liquid (meth)acrylic syrup impregnating        said fibrous substrate,        makes it possible to obtain thermoplastic composite parts with        significantly improved productivity.

Moreover, it has also been discovered that a composite part obtained bythe manufacturing process, is having significantly improved residualmonomer content, due to better conversion of the monomer. The residualmonomer content is less than 5% relative to the quantity of the usedmonomer.

DETAILED DESCRIPTION

According to a first aspect, the present invention relates to

-   -   a liquid composition comprising:    -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2),        said liquid composition is having a dynamic viscosity of between        10 mPa*s and 10 000 mPa*s at 25° C.

According to a second aspect, the present invention relates to a liquidcomposition for impregnating a fibrous substrate, said fibrous substrateconsisting of long fibres, and said liquid composition beingcharacterized in that it comprises:

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2); said liquid (meth)acrylic        syrup having a dynamic viscosity of between 10 mPa*s and 10 000        mPa*s at 25° C.

According to a third aspect, the present invention relates to processfor preparing a liquid composition, said liquid composition is beingcharacterized in that it comprises:

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2); said liquid (meth)acrylic        syrup having a dynamic viscosity of between 10 mPa*s and 10 000        mPa*s at 25° C., by a process comprising the following steps:    -   i) preparing a liquid mixture of (meth)acrylic polymer (P1) and        (meth)acrylic monomer (M1)    -   ii) adding initiators (Ini1) and (Ini2) together or one after        the other to the mixture prepared in the previous step.

According to a fourth aspect, the present invention relates to the useof a liquid composition for impregnating a fibrous substrate, saidfibrous substrate consisting of long fibres, and said liquid compositionbeing characterized in that it comprises:

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2); said liquid (meth)acrylic        syrup having a dynamic viscosity of between 10 mPa*s and 10 000        mPa*s at 25° C.

According to a fifth aspect, the present invention relates to the use ofa liquid composition for manufacturing thermoplastic parts ormanufacturing composite parts, and said liquid composition beingcharacterized in that it comprises:

-   -   a) a (meth)acrylic polymer (P1),    -   b) a (meth)acrylic monomer (M1), and    -   c) two initiators (Ini1) and (Ini2);        said liquid (meth)acrylic syrup having a dynamic viscosity of        between 10 mPa*s and 10 000 mPa*s at 25° C.

According to a sixth aspect, the present invention relates to processfor manufacturing thermoplastic parts by a process comprising thefollowing steps:

-   -   i) preparing a liquid mixture of (meth)acrylic polymer (P1) and        (meth)acrylic monomer (M1)    -   ii) adding initiators (Ini1) and (Ini2) together or one after        the other to the mixture prepared in previous step.    -   iii) putting the liquid (meth)acrylic composition prepared in i)        and ii) in means for polymerization, said composition is being        characterized in that it comprises:        -   a) a (meth)acrylic polymer (P1),        -   b) a (meth)acrylic monomer (M1), and        -   c) two initiators (Ini1) and (Ini2);        -   said liquid (meth)acrylic syrup having a dynamic viscosity            of between 10 mPa*s and 10 000 mPa*s at 25° C.,    -   iv) polymerizing.

According to a seventh aspect, the present invention relates to processfor manufacturing composite parts by a process comprising the followingsteps:

-   -   i) preparing a mixture of (meth)acrylic polymer (P1) and        (meth)acrylic monomer (M1)    -   ii) adding initiators (Ini1) and (Ini2) together or one after        the other to the mixture prepared in previous step.    -   iii) impregnating fibres or fibrous substrate with the liquid        (meth)acrylic composition prepared in i) and ii), said        composition is being characterized in that it comprises:        -   a) a (meth)acrylic polymer (P1),        -   b) a (meth)acrylic monomer (M1), and        -   c) two initiators (Ini1) and (Ini2);        -   said liquid (meth)acrylic syrup having a dynamic viscosity            of between 10 mPa*s and 10 000 mPa*s at 25° C.,    -   iv) polymerizing.

The term “fibrous substrate” as used refers to several fibres, unidirectional rovings or continuous filament mat, fabrics, felts ornonwovens that may be in the form of strips, laps, braids, locks orpieces.

The term “(meth)acrylic” as used refers to any type of acrylic ormethacrylic monomer.

The term “PMMA” as used refers to homo- and copolymers of methylmethacrylate (MMA), the weight ratio of MMA in the PMMA being at least70 wt % for the MMA copolymer.

The term “monomer” as used refers to a molecule that can undergopolymerization.

The term “polymerization” as used refers to the process of converting amonomer or a mixture of monomers into a polymer.

The term “thermoplastic polymer” as used refers to a polymer that turnsto a liquid or becomes more liquid or less viscous of soft when heatedand that can take on new shapes by the application of heat and pressure.This applies also for slightly crosslinked thermoplastic polymers thatcan be thermoformed when heated above the softening temperature.

The term “polymer composite” as used refers to a multicomponent materialcomprising several different phase domains, among which at least onetype of phase domain is a continuous phase and in which at least onecomponent is a polymer.

The term “initiator” as used refers to a compound that canstart/initiate the polymerization of a monomer or monomers.

The term “half life time” t½ as used refers to the time needed for aninitial amount of initiator to decrease concentration in half. This timeis a function of the temperature.

By the abbreviation “phr” is meant weight parts per hundred parts ofcomposition. For example 1 phr of initiator in the composition meansthat 1 kg of initiator is added to 100 kg of composition.

By the abbreviation “ppm” is meant weight parts per million parts ofcomposition. For example 1000 ppm of a compound in the composition meansthat 0.1 kg of compound is present in 100 kg of composition.

By saying that a range from x to y in the present invention, it is meantthat the upper and lower limit of this range are included, equivalent toat least x and up to y.

By saying that a range is between x and y in the present invention, itis meant that the upper and lower limit of this range are excluded,equivalent to more than x and less than y.

The liquid composition or (meth)acrylic syrup according to the inventioncomprises a (meth)acrylic monomer (M1) or a mixture of (meth)acrylicmonomers (M1) and (M1+x), a (meth)acrylic polymer (P1) and at least twoinitiators (Ini1) and (Ini2).

The dynamic viscosity of the liquid composition or (meth) acrylic syrupis in a range from 10 mPa*s to 10000 mPa*s, preferably from 20 mPa*s to7000 mPa*s and advantageously from 20 mPa*s to 5000 mPa*s and moreadvantageously from 20 mPa*s to 2000 mPa*s and even more advantageouslybetween 20 mPa*s and 1000 mPa*s. The viscosity of the syrup can beeasily measured with a Rheometer or viscosimeter. The dynamic viscosityis measured at 25° C. If the liquid (meth) acrylic syrup has a Newtonianbehaviour, meaning no shear thinning, the dynamic viscosity isindependent of the shearing in a rheometer or the speed of the mobile ina viscometer. If the liquid composition has a non-Newtonian behaviour,meaning shear thinning, the dynamic viscosity is measured at a shearrate of 1s⁻¹ at 25° C.

The liquid composition or (meth)acrylic syrup according to theinvention, for impregnating the fibrous substrate, especially comprisesa (meth)acrylic monomer or a mixture of (meth)acrylic monomers, a(meth)acrylic polymer and at least two initiators (Ini1) and (Ini2).

As regards the liquid composition of the invention it comprises a(meth)acrylic monomer (M1), a (meth)acrylic polymer (P1) and at leasttwo initiators (Ini1) and (Ini2). Once polymerized the (meth)acrylicmonomer (M1) is transformed to a (meth)acrylic polymer (P2) comprisingthe monomeric units of (meth)acrylic monomer (M1).

The quantity of two initiators (Ini1) and (Ini2) together in thecomposition is at least 0.1 phr relative to the sum of (meth)acrylicmonomer (M1) and (meth)acrylic polymer (P1). Preferably the quantity oftwo initiators (Ini1) and (Ini2) together in the composition is at least0.2 phr, more preferably at least 0.5 phr, even more preferably at least0.75 phr and advantageously at least 1 phr relative to the sum of(meth)acrylic monomer (M1) and (meth)acrylic polymer (P1).

The quantity of two initiators (Ini1) and (Ini2) together in thecomposition is at most 15 phr of relative to the sum of (meth)acrylicmonomer (M1) and (meth)acrylic polymer (P1). Preferably the quantity oftwo initiators (Ini1) and (Ini2) together in the composition is at most12 phr, more preferably at most 10 phr, even more preferably at most 8phr and advantageously at most 5 phr relative to the sum of(meth)acrylic monomer (M1) and (meth)acrylic polymer (P1).

The quantity two initiators (Ini1) and (Ini2) together in thecomposition is between 0.1 phr and 15 phr relative to the sum of(meth)acrylic monomer (M1) and (meth)acrylic polymer (P1). Preferablythe quantity two initiators (Ini1) and (Ini2) together in thecomposition is between 0.2 phr and 12 phr, more preferably between 0.5phr and 10 phr, even more preferably between 0.75 phr and 8 phr andadvantageously at most between 1 phr and 5 phr relative to the sum of(meth)acrylic monomer (M1) and (meth)acrylic polymer (P1).

As regards the (meth)acrylic monomer (M1), the monomer is chosen fromacrylic acid, methacrylic acid, alkyl acrylic monomers, alkylmethacrylic monomers, hydroxyalkyl acrylic monomers and hydroxyalkylmethacrylic monomers, and mixtures thereof.

Preferably, the (meth)acrylic monomer (M1) is chosen from acrylic acid,methacrylic acid, hydroxyalkyl acrylic monomers, hydroxyalkylmethacrylic monomers, alkyl acrylic monomers, alkyl methacrylic monomersand mixtures thereof, the alkyl group containing from 1 to 22 linear,branched or cyclic carbons; the alkyl group preferably containing from 1to 12 linear, branched or cyclic carbons.

Advantageously, the (meth)acrylic monomer (M1) is chosen from methylmethacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate,methacrylic acid, acrylic acid, n-butyl acrylate, isobutyl acrylate,n-butyl methacrylate, isobutyl methacrylate, cyclohexyl acrylate,cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate,hydroxyethyl acrylate and hydroxyethyl methacrylate, and mixturesthereof.

According to a preferred embodiment, at least 50% by weight andpreferably at least 60% by weight of the (meth)acrylic monomer (M1) ismethyl methacrylate.

According to a first more preferred embodiment, at least 50% by weight,preferably at least 60% by weight, more preferably at least 70% byweight, advantageously at least 80% by weight and even moreadvantageously 90% by weight of the monomer (M1) is a mixture of methylmethacrylate with optionally at least one other monomer.

As regards the (meth)acrylic polymer (P1), mention may be made ofpolyalkyl methacrylates or polyalkyl acrylates. According to a preferredembodiment, the (meth)acrylic polymer is polymethyl methacrylate (PMMA).

The term “PMMA” denotes a methyl methacrylate (MMA) homopolymer orcopolymer or mixtures thereof.

According to one embodiment, the methyl methacrylate (MMA) homo- orcopolymer comprises at least 70%, preferably at least 80%,advantageously at least 90% and more advantageously at least 95% byweight of methyl methacrylate.

According to another embodiment, the PMMA is a mixture of at least onehomopolymer and at least one copolymer of MMA, or a mixture of at leasttwo homopolymers or two copolymers of MMA with a different averagemolecular weight, or a mixture of at least two copolymers of MMA with adifferent monomer composition.

The copolymer of methyl methacrylate (MMA) comprises from 70% to 99.7%by weight of methyl methacrylate and from 0.3% to 30% by weight of atleast one monomer containing at least one ethylenic unsaturation thatcan copolymerize with methyl methacrylate.

These monomers are well known and mention may be made especially ofacrylic and methacrylic acids and alkyl(meth)acrylates in which thealkyl group contains from 1 to 12 carbon atoms. As examples, mention maybe made of methyl acrylate and ethyl, butyl or 2-ethylhexyl(meth)acrylate. Preferably, the comonomer is an alkyl acrylate in whichthe alkyl group contains from 1 to 4 carbon atoms.

According to a first preferred embodiment, the copolymer of methylmethacrylate (MMA) comprises from 80% to 99.7%, advantageously from 90%to 99.7% and more advantageously from 90% to 99.5% by weight of methylmethacrylate and from 0.3% to 20%, advantageously from 0.3% to 10% andmore advantageously from 0.5% to 10% by weight of at least one monomercontaining at least one ethylenic unsaturation that can copolymerizewith methyl methacrylate. Preferably, the comonomer is chosen frommethyl acrylate and ethyl acrylate, and mixtures thereof.

The weight-average molecular mass of the (meth)acrylic polymer (P1)should be high, which means greater than 50 000 g/mol and preferablygreater than 100 000 g/mol.

The weight-average molecular mass can be measured by size exclusionchromatography (SEC).

The (meth)acrylic polymer is fully soluble in the (meth)acrylic monomeror in the mixture of (meth)acrylic monomers. It enables the viscosity ofthe (meth)acrylic monomer or the mixture of (meth)acrylic monomers to beincreased. The solution obtained is generally called a “syrup” or“prepolymer”. The dynamic viscosity value of the liquid (meth)acrylicsyrup is between 10 mPa·s and 10 000 mPa·s. The viscosity of the syrupcan be readily measured with a rheometer or a viscometer. The dynamicviscosity is measured at 25° C.

Advantageously, the liquid (meth)acrylic syrup contains no additionalvoluntarily added solvent.

With regard to the two initiators (Ini1) and (Ini2), the initiatorsgenerate radicals that initiate the monomer(s) to start a radicalpolymerization of the monomer in order to form the polymer chains bypropagation.

Preferably the initiators (Ini1) and (Ini2) are activated by heat.

The heat activated initiators (Ini1) and (Ini2) are preferably radicalinitiators.

The radical initiators (Ini1) and (Ini2) can be chosen from peroxy groupcomprising compound or azo group comprising compounds and preferablyfrom peroxy group comprising compound.

Preferably the peroxy group comprising compound comprises from 2 to 30carbon atoms.

Preferably the peroxy group comprising compound is chosen from diacylperoxides, peroxy esters, peroxydicarbonates, dialkyl peroxides,peroxyacetals, hydroperoxide or peroxyketale.

Preferably the two initiators (Ini1) and (Ini2) have at any giventemperature T1 different half-life times t_(1/2).

Still more preferably the second initiator (Ini2) has at a giventemperature T₁ a half-life time t_(1/2) that is at least two times ofthe half-life time t_(1/2) of the first initiator (Ini1). Even morepreferably the second initiator (Ini2) has at a given temperature T1 ahalf-life time t_(1/2) that is at least three times, advantageously fourtimes, more advantageously five times, still more advantageously sixtimes of the half-life time t_(1/2) of the first initiator (Ini1).

Preferably the temperature T₁ is between 20° C. and 160° C., morepreferably between 40° C. and 140° C. and advantageously between 50° C.and 130° C.

More preferably, the first initiator (Ini1) has a half-life time t_(1/2)of 1 hour at a temperature between 40° C. and 90° C., still morepreferably between 45° C. and 80° C. and even more preferably between50° C. and 75° C.

More preferably, the second initiator (Ini2) has a half-life timet_(1/2) of 1 hour at a temperature of at least 70° C., still morepreferably of at least 75° C.

More preferably, the second initiator (Ini2) has a half-life timet_(1/2) of 1 hour at a temperature between 70° C. and 150° C., stillmore preferably between 75° C. and 140° C. and even more preferablybetween 75° C. and 130° C.

Preferably the difference of the temperature for a given half life timebetween the initiator (Ini2) and (Ini1) is at least 5K. This means iffor a half time t_(1/2) of 1 hour the temperature of (Ini1) is 75° C.,that the temperature of (Ini2) for a half time t_(1/2) of 1 hour is atleast 80° C.

Preferably the difference of the temperature for a given half life timebetween the initiator (Ini2) and (Ini1) is at most 50K. This means iffor a half time t_(1/2) of 1 hour the temperature of Ini1 is 50° C.,that the temperature of Ini2 for a half time t_(1/2) of 1 hour is atmost 100° C.

More preferably the difference of the temperature for a given half timelife between the initiator (Ini2) and (Ini1) is between 5K and 50K andmore preferably between 6K and 40K and even more preferably between 7Kand 30K.

The initiators (Ini2) and (Ini1) are chosen from diisobutyryl peroxide,cumyl peroxyneodecanoate, di(3-methoxybutyl) peroxydicarbonate,1,1,3,3-Tetramethylbutyl peroxyneodecanoate, cumyl peroxyneoheptanoate,di-n-propyl peroxydicarbonate, tert-amyl peroxyneodecanoate,di-sec-butyl peroxydicarbonate, diisopropyl peroxydicarbonate,di(4-tert-butylcyclohexyl) peroxydicarbonate,di-(2-ethylhexyl)-peroxydicarbonate, tert-butyl peroxyneodecanoate,di-n-butyl peroxydicarbonate, dicetyl peroxydicarbonate, dimyristylperoxydicarbonate, 1,1,3,3-tetramethylbutylperoxypivalate, tert-butylperoxyneoheptanoate, tert-amyl peroxypivalate, tert-butylperoxypivalate, di-(3,5,5-trimethylhexanoyl)-peroxide, dilauroylperoxide, didecanoyl peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)-hexane,1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxydiethylacetate, tert-butylperoxyisobutyrate, 1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-di(tert-amylperoxy)cyclohexane,1,1-di-(tert-butylperoxy)-cyclohexane, tert-amylperoxy-2-ethylhexylcarbonate, tert-amyl peroxyacetate, tert-butylperoxy-3,5,5-trimethylhexanoate, 2,2-di-(tert-butylperoxy)-butane,tert-butyl peroxyisopropylcarbonate, tert-butylperoxy-2-ethylhexylcarbonate, tert-amyl peroxybenzoate, tert-butylperoxyacetate, butyl 4,4-di(tert-butylperoxy)valerate, tert-butylperoxybenzoate, di-tert-amylperoxide, dicumyl peroxide,di-(2-tert-butyl-peroxyisopropyl)-benzene,2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane, tert-butylcumyl peroxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, di-tert-butyl peroxide,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane,2,2′-azobis-isobutyronitrile (AIBN), 2,2′-azodi-(2-methylbutyronitrile),azobisisobutyramide, 2,2′-azobis(2,4-dimethylvaleronitrile),1,1′-Azodi(hexahydrobenzonitrile), or 4,4′-azobis(4-cyanopentanoic).

Preferably the initiator (Ini1) is chosen from cumyl peroxyneodecanoate,di(3-methoxybutyl) peroxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumyl peroxyneoheptanoate, di-n-propylperoxydicarbonate, tert-amyl peroxyneodecanoate, di-sec-butylperoxydicarbonate, diisopropyl peroxydicarbonate,di(4-tert-butylcyclohexyl) peroxydicarbonate,di-(2-ethylhexyl)-peroxydicarbonate, tert-butyl peroxyneodecanoate,di-n-butyl peroxydicarbonate, dicetyl peroxydicarbonate, dimyristylperoxydicarbonate, 1,1,3,3-tetramethylbutylperoxypivalate, tert-butylperoxyneoheptanoate, tert-amyl peroxypivalate, tert-butylperoxypivalate, di-(3,5,5-trimethylhexanoyl)-peroxide, dilauroylperoxide, didecanoyl peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)-hexane or1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate.

Preferably the initiator (Ini2) is chosen from tert-amyl peroxypivalate,tert-butyl peroxypivalate, di-(3,5,5-trimethylhexanoyl)-peroxide,dilauroyl peroxide, didecanoyl peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)-hexane,1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxydiethylacetate, tert-butylperoxyisobutyrate, 1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-di(tert-amylperoxy)cyclohexane,1,1-di-(tert-butylperoxy)-cyclohexane, tert-amylperoxy-2-ethylhexylcarbonate, tert-amyl peroxyacetate, tert-butylperoxy-3,5,5-trimethylhexanoate, 2,2-di-(tert-butylperoxy)-butane,tert-butyl peroxyisopropylcarbonate, tert-butylperoxy-2-ethylhexylcarbonate, tert-amyl peroxybenzoate, tert-butylperoxyacetate, butyl 4,4-di(tert-butylperoxy)valerate, tert-butylperoxybenzoate, di-tert-amylperoxide, dicumyl peroxide,di-(2-tert-butyl-peroxyisopropyl)-benzene,2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane, tert-butylcumyl peroxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, di-tert-butyl peroxide or3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.

The weight ratio between the two initiators (Ini2) and (Ini1) is between1/10 and 10/1, preferably between 1/5 and 5/1 and more preferablybetween 1/4 and 4/1.

Preferably the initiator (Ini1) is chosen from peroxydicarbonates.Preferably the initiator (Ini1) has a maximal storage temperature of 20°C. or less, preferably of 15° C. or less.

More preferably the initiator (Ini1) has following general formula (1):

wherein R₁ and R₂ each present and alkyl group, that could be linear,branched or cyclic, or a combination of the three, having at least 6carbon atoms, preferably 8 carbon atoms and more preferably at least 10carbon atoms. Advantageously the groups R₁ and R₂ each have between 10and 30 carbon atoms and more advantageously between 10 and 20 carbonatoms. The groups R₁ and R₂ can be different or identical.

Even more preferably the initiator (Ini1) is chosen fromdi(4-tert-butylcyclohexyl) peroxydicarbonate, dicetyl peroxydicarbonateand dimyristyl peroxydicarbonate and initiator (Ini2) is chosen frombenzoyl peroxide, t-butylperoxy 2-ethylhexanoate, dilauroyl peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexane and didecanoylperoxide.

In a first even more preferred embodiment the initiator (Ini1) is chosenfrom di(4-tert-butylcyclohexyl) peroxydicarbonate.

The initiator (Ini2) in this first even more preferred embodiment ischosen from benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, dilauroylperoxide and didecanoyl peroxide.

In a second even more preferred embodiment the initiator (Ini1) ischosen from dicetyl peroxydicarbonate.

The initiator (Ini2) in this second even more preferred embodiment ischosen from benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, dilauroylperoxide and didecanoyl peroxide.

In a third even more preferred embodiment the initiator (Ini1) is chosenfrom dimyristyl peroxydicarbonate.

The initiator (Ini2) in this third even more preferred embodiment ischosen from benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, dilauroylperoxide and didecanoyl peroxide

In order to conserve a dynamic viscosity of the liquid composition or(meth)acrylic syrup, also that it allows good impregnation of thefibrous substrate if necessary, and to conserve the thermoplasticproperties of the matrix obtained after polymerization of the fibroussubstrate preimpregnated with syrup, the compounds of the syrup areincorporated in the following mass percentages:

The (meth)acrylic monomer(s) (M1) in the liquid composition or(meth)acrylic syrup are present in proportions of between 40% and 90% byweight and preferably between 45% and 85% by weight of the compositioncomprising (meth)acrylic monomer(s) (M1) and (meth)acrylic polymer (P1).

The (meth)acrylic polymer(s) (P1) in the liquid composition or(meth)acrylic syrup are present in a proportion of at least 1% byweight, preferably at least 5% and advantageously at least 10% by weightof the composition comprising (meth)acrylic monomer(s) (M1) and(meth)acrylic polymer (P1).

The (meth)acrylic polymer(s) (P1) in the liquid (meth)acrylic syrup arepresent in a proportion of not more than 50% by weight, preferably notmore than 40% and advantageously not more than 30% by weight of thecomposition comprising (meth)acrylic monomer(s) (M1) and (meth)acrylicpolymer (P1).

All the optional additives and fillers are added to the liquid(meth)acrylic syrup before the impregnation and or polymerization.

The liquid composition according to the invention can comprise optimallyas well activator for polymerization.

The polymerization activator or accelerator is chosen from tertiaryamines such as N,N-dimethyl-p-toluidine (DMPT),N,N-dihydroxyethyl-p-toluidine (DHEPT), organic-soluble transition metalcatalysts or mixtures thereof.

Advantageously the liquid (meth) acrylic composition contains no metalbased catalysts. No metal comprising additives as activators forcatalytically accelerate the polymerization reaction are added to liquid(meth) acrylic composition according to the invention. These concernsespecially tin based compounds as tin chloride.

The content of the activator with respect to the (meth)acrylic monomer(M1) of the liquid (meth) acrylic composition is from 100 ppm to 10000ppm (by weight), preferably from 200 ppm to 7000 ppm by weight andadvantageously from 300 ppm to 4000 ppm.

As regards the process for manufacturing the liquid composition or(meth)acrylic syrup, a first step consists in preparing a first syrupcomprising the (meth)acrylic monomer (M1) or mixture of (meth)acrylicmonomers and a (meth)acrylic polymer (P1). The initiators (Ini2) and(Ini1) are then added to the syrup, in the proportions indicated aboveto conserve a dynamic viscosity of between 10 mPa*s and 10 000 mPa*s, at25° C.

Preferably the (meth)acrylic polymer (P1) is added to the (meth)acrylicmonomers and solubilized.

The initiators (Ini2) and (Ini1) can be added together or apart oneafter the other. If added apart the order is not of importance.

Preferably the initiators (Ini2) and (Ini1) are added at a temperatureTadd below 50° C., more preferably below 40° C., advantageously below30° C. and more advantageously below 25° C.

The liquid composition according to the invention, detailed in previousparagraphs, can be used for impregnating fibres or fibrous substrate orfor manufacturing thermoplastic parts or manufacturing composite parts.

As regards the process for impregnating the fibres or fibrous substrate,it comprises a step of impregnating the fibrous substrate with theliquid composition or (meth)acrylic syrup.

This impregnation step can take place in a mold or closed mold or abath.

If the viscosity of the liquid (meth)acrylic syrup at a giventemperature is slightly too high for the impregnation process, it ispossible to heat the syrup so as to have a more liquid syrup forsufficient wetting and correct and complete impregnation of the fibroussubstrate.

As regards the fibrous substrate, mention may be made of several fibres,uni directional rovings or continuous filament mat, fabrics, felts ornonwovens that may be in the form of strips, laps, braids, locks orpieces. The fibrous material may have various forms and dimensions,either one-dimensional, two-dimensional or three-dimensional. A fibroussubstrate comprises an assembly of one or more fibres. When the fibresare continuous, their assembly forms fabrics.

The one-dimensional form corresponds to linear long fibres. The fibresmay be discontinuous or continuous. The fibres may be arranged randomlyor parallel to each other, in the form of a continuous filament. A fibreis defined by its aspect ratio, which is the ratio between the lengthand diameter of the fibre. The fibres used in the present invention arelong fibres or continuous fibres. The fibres have an aspect ratio of atleast 1000, preferably at least 1500, more preferably at least 2000,advantageously at least 3000 and more advantageously at least 5000, evenmore advantageously at least 6000, more advantageously still at least7500 and most advantageously at least 10 000.

The two-dimensional form corresponds to nonwoven or woven fibrous matsor reinforcements or bundles of fibres, which may also be braided. Evenif the two-dimensional form has a certain thickness and consequently inprinciple a third dimension, it is considered as two-dimensionalaccording to the present invention.

The three-dimensional form corresponds, for example, to nonwoven fibrousmats or reinforcements or stacked or folded bundles of fibres ormixtures thereof, an assembly of the two-dimensional form in the thirddimension.

The origins of the fibrous material may be natural or synthetic. Asnatural material one can mention plant fibres, wood fibres, animalfibres or mineral fibres.

Natural fibres are, for example, sisal, jute, hemp, flax, cotton,coconut fibres, and banana fibres. Animal fibres are, for example, woolor hair.

As synthetic material, mention may be made of polymeric fibres chosenfrom fibres of thermosetting polymers, of thermoplastic polymers ormixtures thereof.

The polymeric fibres may consist of polyamide (aliphatic or aromatic),polyester, polyvinyl alcohol, polyolefins, polyurethanes, polyvinylchloride, polyethylene, unsaturated polyesters, epoxy resins and vinylesters.

The mineral fibres may also be chosen from glass fibres, especially ofE, R or S2 type, carbon fibres, boron fibres or silica fibres.

The fibrous substrate of the present invention is chosen from plantfibres, wood fibres, animal fibres, mineral fibres, synthetic polymericfibres, glass fibres and carbon fibres, and mixtures thereof.

Preferably, the fibrous substrate is chosen from mineral fibres.

The fibres of the fibrous substrate have a diameter between 0.005 μm and100 μm, preferably between 1 μm and 50 μm, more preferably between 5 μmand 30 μm and advantageously between 10 μm and 25 μm.

Preferably, the fibres of the fibrous substrate of the present inventionare chosen from continuous fibres (meaning that the aspect ratio doesnot necessarily apply as for long fibres) for the one-dimensional form,or for long or continuous fibres for the two-dimensional orthree-dimensional form of the fibrous substrate.

According to another additional aspect, the invention relates to apolymeric composite material comprising a thermoplastic (meth)acrylicmatrix and a fibrous substrate used as reinforcement, in which thefibrous substrate consists of long fibres, said composite material beingcharacterized in that the thermoplastic (meth)acrylic matrix is obtainedafter polymerization of said fibrous substrate preimpregnated with saidliquid composition according to the invention or (meth)acrylic syrup.

Another aspect of the present invention is a process for manufacturingmechanical or structured parts or products, comprising the followingsteps:

-   -   i) impregnating a fibrous substrate with the liquid composition        or (meth)acrylic syrup according to the invention,    -   ii) polymerizing the liquid composition or (meth)acrylic syrup        impregnating said fibrous substrate.

The polymerization of the liquid composition or (meth)acrylic syrup thathas impregnated the fibrous substrate during the process formanufacturing mechanical or structured parts or products during stepii), takes place at temperature between 80° C. and 140° C., preferablybetween 90° C. and 130° C. The polymerization step ii) is more or lessisotherm. By isotherm is meant in the present invention that thetemperature during polymerization is kept in an interval of ΔT of 20K ofthe polymerization temperature and comprises no temperature ramps, wherethe temperature is for example decreased during polymerization orincreased at the end and the difference of temperature duringpolymerization is more than 20K. For example the impregnated the fibroussubstrate is heated up to 100° C. and the temperature at the end doesnot exceed 120° C. Or for example the impregnated the fibrous substrateis heated up to 100° C. and the temperature during the polymerizationstep stays inside an interval of 20K: between 90° C. and 110° C. or alsobetween 95° C. and 115° C.

Advantageously the polymerization temperature is kept in an interval ofΔT of 18K, more advantageously of 16K, even more advantageously of 14K,still more advantageously of 12K and most advantageously of 10K.

As regards the process for manufacturing composite parts, but alsomechanical or structured parts or products, various processes could beused for preparing these parts. Mention may be made of vacuum assistedresin infusion (VARI), pultrusion, vacuum bag molding, pressure bagmolding, autoclave molding, resin transfer molding (RTM) and variationsthereof as (HP-RTM, C-RTM, I-RTM), reaction injection molding (RIM),reinforced reaction injection molding (R-RIM) and variants thereof,press molding, compression molding, liquid compression molding (LCM) orsheet molding compound (SMC) or bulk molding compound (BMC).

A first preferred manufacturing process for manufacturing compositeparts are processes according to which the liquid composition istransferred to the fibrous substrate by impregnation of the fibroussubstrate in a mold. The processes requiring a mold a listed above andcomprise the wording molding.

A second preferred manufacturing process for manufacturing compositeparts are processes according to which the liquid composition is used inpultrusion process. The fibres are guided through a resin batchcomprising the composition according to the invention. The fibres asfibrous substrate are for example in form of a unidirectional roving ora continuous filament mat. After impregnation in the resin bath thewetted fibres are pulled through a heated die, where polymerizationtakes place.

A third preferred manufacturing process is vacuum assisted resininfusion (VARI).

The process for manufacturing composite parts, but also mechanical orstructured parts or products, can additionally comprise the step of postforming. The post forming includes bending as changing the form of thecomposite part.

The process for manufacturing composite parts, but also mechanical orstructured parts or products, can additionally comprise the step ofwelding or gluing or laminating.

The thermoplastic composite parts obtained from the processes accordingto the invention can be post formed after polymerization of the liquidcomposition of the invention. The forming includes bending as changingthe form of the composite.

The thermoplastic parts or manufactured composite parts obtained afterpolymerization of the liquid composition of the invention and/or fromthe processes according to the invention can be welded, glued orlaminated.

As regards the use of the mechanical parts made of composite materialthus manufactured, mention may be made of automotive applications,transport applications such as buses or lorries, nautical applications,railroad applications, sport, aeronautic and aerospace applications,photovoltaic applications, computer-related applications, constructionand building applications, telecommunication applications and windenergy applications.

The mechanical part made of composite material is especially a motorvehicle part, boat part, bus part, train part, sport article, plane orhelicopter part, space ship or rocket part, photovoltaic module part, amaterial for construction or building for example composite rebars,dowels and stirrups for civil engineering and high rise construction,wind turbine part for example spar cap of girder of wind turbine blade,furniture part, construction or building part, telephone or cellphonepart, computer or television part, or printer or photocopier part.

In a first preferred embodiment the mechanical part made of compositematerial is especially a material for construction or building forexample composite rebars, dowels and stirrups for civil engineering andhigh rise construction.

In a second preferred embodiment the mechanical part made of compositematerial is especially a wind turbine part for example a spar cap ofgirder of wind turbine blade.

EXAMPLES

First Step: Preparation of a Liquid Composition or the (Meth)AcrylicSyrup

A liquid composition is prepared by dissolving 25% by weight of the PMMA(BS520, a copolymer of MMA comprising ethyl acrylate as comonomer) as(P1) in 75% by weight of methyl methacrylate as (M1), which isstabilized with HQME (hydroquinone monomethyl ether).

To this liquid composition are added different initiators (Ini1) only ormixtures of two different initiators (Ini1) and (Ini2). As initiators(Ini1) or (Ini2) are used di(4-tert-butylcyclohexyl) peroxydicarbonate(P16—Perkadox® 16 from the company Akzo Nobel), benzoyl peroxide(BPO—Perkadox® CH50X from the company Akzo Nobel), t-butylperoxy2-ethylhexanoate (TBPO—Luperox® 26 from the company Arkema), dilauroylperoxide (LP—Luperox® LP from the company Arkema) and didecanoylperoxide (DEC—Luperox® DEC from the company Arkema).

The comparative examples have no mixture of two initiators (Ini1) and(Ini2) according to the invention.

Second Step: Polymerization of a Liquid Composition or the (Meth)AcrylicSyrup

Polymerization of respective compositions is made by adding to 100 partsby weight of the liquid composition (based on (M1) and (P1) only) theinitiator or the initiators as indicated in table 1. The respectivecomposition are heated up to 110° C. in a metallic press under apressure of 10 bars.

The time up to 95% conversion of the respective samples is measured andgiven in table 1 for each composition.

TABLE 1 compositions and results at 110° C. Ini1 Ini2 time [phr] [phr][s] Comparative P16 — No complete example 1 2 polymerization*Comparative — LP 302 example 2 2 Comparative P16 — No complete example 33 polymerization* Example 1 P16 BPO 166 2 1 Example 2 P16 DEC 142 2 1Example 3 P16 LP 159 2 1 Example 4 P16 TBPO 170 2 1 Example 5 P16 DEC164 1 2 Example 6 P16 LP 180 1 2 Example 7 P16 TBPO 174 1 2 *Conversionless than 50%

The decrease of polymerization time in table 1 for the examplessignifies a better kinetics, faster polymerization, while having a goodconversion. Comparative examples 1 and 3 has a conversion of less than50% at 110° C., and a good conversion and faster polymerization has beenobtained by having two initiators (see examples 1 to 7) in comparison tocomparative example 2.

The invention claimed is:
 1. A liquid composition comprising, a) a(meth)acrylic polymer (P1), b) a (meth)acrylic monomer (M1), and c) twodifferent initiators (Ini1) and (Ini2) having at any given temperatureT₁ different half-life times t_(1/2), said liquid composition is havinga dynamic viscosity of between 10 mPa*s and 10,000 mPa*s at 25° C.,wherein the quantity of said two initiators (Ini1) and (Ini2) togetherin the composition is between 0.75 phr and 15 phr relative to the sum ofthe (meth)acrylic monomer (M1) and (meth)acrylic polymer (P1), andwherein the two initiators (Ini1) and (Ini2) are selected from the groupconsisting of diacyl peroxides, peroxy esters, peroxydicarbonates,dialkyl peroxides, peroxyacetals, hyperperoxide, and peroxyketale, andwherein the first initiator (Ini1) has a half-life time t_(1/2) of 1hour at a temperature between 40° C. and 90° C., and wherein the secondinitiator (Ini2) has a half-life time t_(1/2) of 1 hour at a temperatureof at least 70° C.
 2. The liquid composition as claimed in claim 1,wherein the quantity of said two initiators (Ini1) and (Ini2) togetherin the composition is between 0.75 phr and 8 phr relative to the sum of(meth)acrylic monomer (M1) and (meth)acrylic polymer (P1).
 3. The liquidcomposition according to claim 1, wherein the second initiator (Ini2)has at a given temperature T₁ a half-life time t_(1/2) that is at leasttwo times of the half-life time t_(1/2) of the first initiator (Ini1).4. The liquid composition according to claim 1, wherein the secondinitiator (Ini2) has at a given temperature T₁ a half-life time t_(1/2)that is at least six times of the half-life time t_(1/2) of the firstinitiator (Ini1).
 5. The liquid composition according to claim 1,wherein the first initiator (Ini1) has a half-life time t_(1/2) of 1hour at a temperature between 45° C. and 80° C.
 6. The liquidcomposition according to claim 1, wherein the second initiator (Ini2)has a half-life time t_(1/2) of at least 1 hour at a temperature of atleast 75° C.
 7. The liquid composition according to claim 1, wherein thedifference of the temperature for a given half time life between theinitiator (Ini2) and (Ini1) is between 5K and 50K.
 8. The liquidcomposition according to claim 1, wherein the weight ratio between thetwo initiators (Ini2) and (Ini1) is between 1/10 and 10/1.
 9. The liquidcomposition according to claim 1, wherein the two initiators (Ini1) and(Ini2) are selected from the group consisting of diisobutyryl peroxide,cumyl peroxyneodecanoate, di(3-methoxybutyl) peroxydicarbonate,1,1,3,3-Tetramethylbutyl peroxyneodecanoate, cumyl peroxyneoheptanoate,di-n-propyl peroxydicarbonate, tert-amyl peroxyneodecanoate,di-sec-butyl peroxydicarbonate, diisopropyl peroxydicarbonate,di(4-tert-butylcyclohexyl) peroxydicarbonate,di-(2-ethylhexyl)-peroxydicarbonate, tert-butyl peroxyneodecanoate,di-n-butyl peroxydicarbonate, dicetyl peroxydicarbonate, dimyristylperoxydicarbonate, 1,1,3,3-tetramethylbutylperoxypivalate, tert-butylperoxyneoheptanoate, tert-amyl peroxypivalate, tert-butylperoxypivalate, di-(3,5,5-trimethylhexanoyl)-peroxide, dilauroylperoxide, didecanoyl peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)-hexane,1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxydiethylacetate, tert-butylperoxyisobutyrate, 1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-di(tert-amylperoxy)cyclohexane,1,1-di-(tert-butylperoxy)-cyclohexane, tert-amylperoxy-2-ethylhexylcarbonate, tert-amyl peroxyacetate, tert-butylperoxy-3,5,5-trimethylhexanoate, 2,2-di-(tert-butylperoxy)-butane,tert-butyl peroxyisopropylcarbonate, tert-butylperoxy-2-ethylhexylcarbonate, tert-amyl peroxybenzoate, tert-butylperoxyacetate, butyl 4,4-di(tert-butylperoxy)valerate, tert-butylperoxybenzoate, di-tert-amylperoxide, dicumyl peroxide,di-(2-tert-butyl-peroxyisopropyl)-benzene,2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane, tert-butylcumyl peroxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, di-tert-butyl peroxide,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane,2,2′-azobis-isobutyronitrile (AIBN), 2,2′-azodi-(2-methylbutyronitrile),azobisiso-butyramide, 2,2′-azo-bis(2,4-dimethylvaleronitrile),1,1′-Azodi(hexahydrobenzonitrile), and 4,4′-azobis(4-cyanopentanoic).10. The liquid composition according to claim 1, wherein the initiator(Ini1) is a peroxydicarbonate.
 11. The liquid composition according toclaim 1, wherein the initiator (Ini1) has the following general formula(1):

wherein R₁ and R₂ each are present and said alkyl group could be linear,branched or cyclic, or a combination of the three, having at least 6carbon atoms.
 12. The liquid composition according to claim 11, whereinthe groups R₁ and R₂ each have between 10 and 30 carbon atoms.
 13. Theliquid composition according to claim 1, wherein the initiator (Ini1) ischosen from di(4-tert-butylcyclohexyl) peroxydicarbonate, dicetylperoxydicarbonate and dimyristyl peroxydicarbonate and initiator (Ini2)is chosen from benzoyl peroxide, t-butylperoxy 2-ethylhexanoate,dilauroyl peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexaneand didecanoyl peroxide.
 14. The liquid composition according to claim1, wherein the initiator (Ini1) is chosen fromdi(4-tert-butylcyclohexyl) peroxydicarbonate and initiator (Ini2) ischosen from benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, dilauroylperoxide and didecanoyl peroxide.
 15. The liquid composition accordingto claim 1, wherein the initiator (Ini1) is chosen from dicetylperoxydicarbonate and initiator (Ini2) is chosen from benzoyl peroxide,t-butylperoxy 2-ethylhexanoate, dilauroyl peroxide and didecanoylperoxide.
 16. The liquid composition according to claim 1, wherein theinitiator (Ini1) is chosen from dimyristyl peroxydicarbonate andinitiator (Ini2) is chosen from benzoyl peroxide, t-butylperoxy2-ethylhexanoate, dilauroyl peroxide and didecanoyl peroxide.
 17. Theliquid composition according to claim 1, wherein the (meth)acrylicpolymer (P1) comprises at least 50% by weight of methyl methacrylate(MMA).
 18. The liquid composition according to claim 1, characterized inthat the (meth)acrylic monomer (M1) is selected from the groupconsisting of acrylic acid, methacrylic acid, alkyl acrylic monomers andalkyl methacrylic monomers, and mixtures thereof, the alkyl groupcontaining from 1 to 22 linear, branched or cyclic carbons; the alkylgroup preferably containing from 1 to 12 linear, branched, and cycliccarbons.
 19. The liquid composition as claimed in claim 18, wherein the(meth)acrylic monomer is chosen from methyl methacrylate, ethylmethacrylate, methyl acrylate, ethyl acrylate, methacrylic acid, acrylicacid, n-butyl acrylate, isobutyl acrylate, n-butyl methacrylate,isobutyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate,isobornyl acrylate and isobornyl methacrylate, and mixtures thereof. 20.An impregnation process for impregnating a fibrous substrate, saidfibrous substrate consisting of fibres having an aspect ratio of atleast 1000, wherein said process comprises a step of impregnating saidfibrous substrate with liquid composition according to claim 1.